Weird sounds when I press the brakes only. 2009 Prius with 200k.

Up until Tombukt2 started posting about the stroke simulator in this thread, I had never seen anybody, even once, talking about any issue with a stroke simulator. It's a dead-simple cylinder with a piston on a spring in it. There's a valve that turns it on and off. That's it. I'd be surprised if it had anything at all to do with your issue.

Have you had a chance to make the recording you said you'd make a few days ago? That probably would help us more.

 

The sound I notice in that video kinda sounds like a hog rooting around, right?

I'm going with actuator. A target pressure isn't being held steadily, and the ECU is goosing some valves as needed to keep it at target.

 

The video linked in #24 has the sound of the booster pump running. When the pump runs excessively, or repeatedly runs by itself, that can be a sign of (a different kind of) actuator problem. Ironically, in the video in #24, I'm not convinced there is any problem; the person is pumping the brakes a few times to make the pump run, and for the pump to run every few times the brakes are used is perfectly normal.

So hearing the sound of the pump is only a sign of a problem if you are hearing it repeating too often or at the 'wrong' times. Otherwise it isn't a problem sound at all.

The earlier video in #22 gives the sound of the brake system re-applying pressure in small spurts, to make up for pressure that is not holding at target. That's just a different kind of issue. The brake actuator is complicated machinery that doesn't have just one way to 'fail'.

If you have a scan tool that shows live data, you might get an independent check on my ear by watching the pressure sensor readings while you are holding the pedal down and hearing that repeated hog-rooting noise. If my ear isn't mistaken, you'll see one of the pressure readings kind of declining, and jumping back up a bit with each hog-root.

Assuming that's what's happening, the likely cause is a leak. If the leak is external (brake fluid leaving the system), it might be something quite easy to solve; you look for where it's leaking out, and fix that. In the case of an external leak, you'd expect the fluid level in your reservoir to be dropping over time, and something under your car to be wet with brake fluid.

A more common case is an internal leak, where one of the valves in the actuator isn't seating perfectly, and fluid is staying in the system, but just escaping back into the reservoir.

 

I agree with ChapmanF, don't replace anything until you see codes or has issues with stopping the car. Once those ABS, VSC and/or engine light turns on then it's time to properly diagnose. There are mechanical noises you hear but that didn't trigger the sensors for any anomaly. Money-wise it's going to be frustrating blindly replacing parts without knowing the source of the issue (or just go with an expensive guess).

 

Post #25 also suggested some checks you can do to independently satisfy yourself as to what is going on. Watching for the pressure variation is easy if you have a suitable scan tool (which you would need to complete a repair anyway), and checking for external leaks is also not rocket science.

I'm not sure I ever said don't replace anything until you see codes or [have] issues with stopping the car; for me, issues stopping the car mean a repair has been put off too long. But I am in favor of gathering info and using the available time wisely to plan and budget a repair.

 

I just wanted to chime in I experienced that same exact sound posted here:

The scenario to consistently get there was always when I was stationary.
Depending how much "pressure" I applied to the brakes, is what made the sound come on. If I applied a lot of pressure I can make it keep grinding away and if I apply less pressure it stops.

I did get my ABS actuator replaced at the dealership and I thought that fixed it but now that it's cold outside again the sound is coming back. I had my actuator replaced 6 months ago. So if you do the parts cannon approach I don't think replacing the actuator is going to fix it I think it's something else.

My old actuator was FINE, it worked fine it and it didn't run excessively hinting at a failing actuator. I just thought the weird sound was the actuator grinding away and that was a sign it was failing but I think it's a different part. I haven't looked into it much since then.

1. When braking at speed there is no sound of the grinding sound
2. The grinding sound only happens when stationary and applying A LOT of pressure to the brake pedal. Think slamming on your brakes.
3. I've slammed on my brakes in traffic and it doesn't make a grinding sound, it just works.

At this point I've just accepted my car grinds when stationary when applying a heavy foot. If you find a resolution I'll be watching!

 

That "dolphin under the hood" noise isn't anything grinding. Sometimes we call it a grunt, bark, honk, or quack noise.

It is the sound of brake fluid being let in small amounts through a slightly-open valve.

If it keeps happening like that while you're just holding the pedal down, it is the computer for the brakes giving that valve a little touch over and over again to send a little more fluid toward the brakes, trying to hold a target pressure that isn't holding steady.

When the pressure won't hold steady, it's either because of an external leak (brake fluid seeping out of the system, you should find a wet spot somewhere, and eventually the reservoir level looks lower) or because of an internal leak (no brake fluid leaves the system, just sneaks back to the reservoir from a circuit where it should be under pressure).

 

Any updates?
Mine has been doing it intermittently for a year now. Less so on warmer days. I notice my brakes feel grabbier in this gen 2 than my last one.

No codes are being thrown and no performance changes other than feeing a bit grabby. Toyota said the brakes look fine.
I’m looking to sell soon too and don’t know how to proceed.